Bench flatness

[James Lehr]

So I've wrestled my benchtop for the last month and I'm finally making progress. I used winding sticks today and everything looks good. However, when I use my No 7 Stanley to check for flat across the width I can see small amounts (1 cm or less) of light coming through. I used my framing square with similar results. I don't own any measuring tool that is 24" long and guaranteed straight. My question is how "flat" do I need the top to achieve a reliable reference surface for planing? I am planning a lot of hand tool work making jewelry boxes, furniture, and toys. I'm frustrated bc my jointer sole measured flat to me ( about .0005) or so with a feeler gauge all around not able to slip under the sole. But I still see surface variation under the measuring tool all along the length of the benchtop measuring across the width. I will admit to being somewhat obsessive about exactness.

[bridger berdel]

The larger, thinner, more flexible the boards you are planing the more it matters to remove small local variations in your bench top. I'd say go ahead and start making your projects, keeping an eye on how your thinner more flexible workpieces are behaving as you flatten them. Wood moves around so it may take a few projects made with careful attention paid to detect small out of flatness of your bench top

[Jim Koepke]

...
However, when I use my No 7 Stanley to check for flat across the width I can see small amounts (1 cm or less) of light coming through.

...

I'm frustrated bc my jointer sole measured flat to me ( about .0005) or so with a feeler gauge all around not able to slip under the sole. But I still see surface variation under the measuring tool all along the length of the benchtop measuring across the width. I will admit to being somewhat obsessive about exactness.

You may be seeing the evidence left by a cambered blade or the tracks from a straight blade digging at the edge.

If you have a little dip of about of a thousands or two you shouldn't have a problem. Make a project or two and see if you notice.

Some people actually use a toothing plane to roughen the surface of their workbenches. Not something I recommend.

jtk

[jamie shard]

This can be kind of eye opening: take your best straightedge/surface and then use feeler gauges underneath to check the actual variation on the table top. It's kind of fun to create a topo map of countour lines. Be sure to rotate the straightedge, holding one end and then the other. Where it pivots are the highest points of the bench.

If you don't have a straight edge, now is the chance to make one. Use your best jointer and set it for a very fine cut. Take a 24" piece of edge grain/quartersawn wood, plane out the middle of the board, leaving about a half inch unplaned on either end, until it stops cutting. At this point, you have a hollow over the length of the board about the depth of the cut (one or two thousands). Now take one full (or maybe two) passes along the entire length. You are now within a thousandth of a straightedge, good enough!

[jamie shard]

by the way... light is really thin, so you pretty much will always have some sneaking through. :D

[Prashun Patel]

I'd make a longer flat straight edge. Make two and use them to check each other. I've found (through trial and error) that the easiest (albeit most tedious) way to make a long straight edge is to use shorter ones to make it. So, use your jointer to make a 24" edge, then use that to make a 36", etc.

[bridger berdel]

I'd make a longer flat straight edge. Make two and use them to check each other. I've found (through trial and error) that the easiest (albeit most tedious) way to make a long straight edge is to use shorter ones to make it. So, use your jointer to make a 24" edge, then use that to make a 36", etc.



It's time for...... TA DA!

the three strait edge bootstrap (http://books.google.com/books?id=oEJVAAAAMAAJ&pg=PA151&lpg=PA151&dq=three+straightedge+method&source=bl&ots=xaBclUiy3T&sig=dQIORcBgFW529oQdRQ8eTMLNuVU&hl=en&sa=X&ei=Bpl8VI-YC5evoQTSuoH4BQ&ved=0CEQQ6AEwBg#v=onepage&q=three%20straightedge%20method&f=false)!

[Andrae Covington]

...I can see small amounts (1 cm or less) of light coming through...

I assume you mean 1cm wide, not deep. Sounds flat enough to me, but everyone has different standards. Think about a corrugated plane sole: if you put a straightedge to it and hold it up to the light, you will see light shine through the grooves, but they're so narrow the sole is effectively flat. As long as your workpieces are wide enough to span narrow hollows like that, then it's flat enough.

[Frederick Skelly]

http://www.sawmillcreek.org/showthread.php?214798-Newbie-Notes-Lessons-learned-while-flattening-my-workbench

James - maybe this thread will help you some.
Fred

[James Lehr]

http://www.sawmillcreek.org/showthread.php?214798-Newbie-Notes-Lessons-learned-while-flattening-my-workbench

James - maybe this thread will help you some.
Fred

Awesome me thread link! Thank you. I've given up the flattening for now. I've started some projects and the boards seem flatter now so I think mission accomplished.

[Jim Matthews]

If absolute flatness is required, you can always build an accessory top.

I'm not convinced that a benchtop needs to be more closer than 1/64" accurately flat.
It's a giant clamp, not an telescope lens.

Search torsion box top for alternatives, if it becomes necessary.

[Daniel Rode]

My benchtop is generally flat. It's not perfect. There's a little dip in one area a tiny hump in another. That was as flat as I could make it at the time and it's still good enough. Nothing is off by 1/64" but I it's not a reference surface I trust. I still use my table saw top or jointer bed to test for flatness, but I'd like my bench to be a reliable guide as well.

I'm a bit more experienced with planing, so I might try to get it a little flatter over the holiday break.

I'll miss the work-worn and stained surface, though.